Projection image display

ABSTRACT

A white light beam from a light source portion ( 201 ) is separated into respective light beams of red, green and blue by a color separation optical system ( 204 ). The respective light beams are reflected by a rotating polygon mirror ( 207 ), travel via a second optical system ( 210 ) and form belt-like illuminated regions on an image display panel ( 212 ). By a rotation of the rotating polygon mirror ( 207 ), the illuminated regions of the respective light beams move continuously, and each pixel of the image display panel ( 212 ) is driven by a signal corresponding to a color of light entering this pixel. An image on the image display panel ( 212 ) is magnified and projected onto a screen by a projection optical system ( 216 ). The color separation optical system ( 204 ) has first and second reflecting mirrors that respectively reflect the respective light beams of red, green and blue, and these reflecting mirrors are arranged so that optical paths of the respective light beams have equal lengths from the light source portion ( 201 ) to the rotating polygon mirror ( 207 ). This makes it possible to provide a small projection-type image display apparatus that has a high efficiency of light utilization and can display an image with high resolution and enhanced color uniformity.

TECHNICAL FIELD

[0001] The present invention relates to a projection-type image displayapparatus that displays a color image with one light valve serving as amodulating member.

BACKGROUND ART

[0002] A liquid crystal projector that now is the mainstream in themarket of large-screen displays uses a light source lamp, a focusinglens and a projection lens to magnify and form an image of a liquidcrystal panel (a light valve) onto a screen. Current commercial systemscan be classified roughly into a three-plate system and a single-platesystem.

[0003] In the former system of the three-plate liquid crystal projector,after a light beam from a white light source is separated into lightbeams of three primary colors of red, green and blue by a colorseparation optical system, these light beams are modulated by threemonochrome liquid crystal panels so as to form images of the threeprimary colors. Thereafter, these images are combined by a colorcombination optical system so as to be projected onto a screen by oneprojection lens. Since the entire spectrum of the white light from thelight source can be utilized, this system has a high efficiency of lightutilization. However, because of the necessity of the three liquidcrystal panels, the color separation optical system, the colorcombination optical system and a convergence adjusting mechanism betweenthe liquid crystal panels, this system is relatively expensive.

[0004] On the other hand, a conventional single-plate system liquidcrystal projector is compact and inexpensive because an image formed ona liquid crystal panel having a mosaic color filter simply is magnifiedand projected onto a screen. However, since this system obtains lightwith a desired color by absorbing light with an unwanted color out ofwhite light from the light source by means of the color filter servingas a color selection member, only one-third or less of the white lightthat has entered the liquid crystal panel is transmitted (or reflected).Accordingly, the efficiency of light utilization is low andhigh-brightness images cannot be obtained easily. When the light sourceis brightened, the brightness of the displayed image can be improved.However, there remain problems of heat generation and light resistanceowing to light absorption by the color filter, making it very difficultto increase the brightness.

[0005] A single-plate system that improves the efficiency of lightutilization is suggested in JP 4(1992)-316296 A. FIG. 8 shows aschematic configuration of this image display apparatus.

[0006] A white light beam emitted from a light source portion 100 is ledto a color separation optical system 101. As shown in FIG. 9, the colorseparation optical system 101 includes dichroic mirrors 121 a and 121 band two reflection mirrors 121 c and 121 d. The dichroic mirror 121 areflects blue light and transmits green light and red light. Thedichroic mirror 121 b reflects red light and transmits green light andblue light. These dichroic mirrors 121 a and 121 b are crossed. A bluelight beam 132 out of a white light beam 131 from the light sourceportion 100 is reflected by the dichroic mirror 121 a, reflected by thereflection mirror 121 d and passes through an aperture 102B of a fieldstop 102. A red light beam 133 is reflected by the dichroic mirror 121b, reflected by the reflection mirror 121 c and passes through anaperture 102R of the field stop 102. A green light beam 134 istransmitted by both the dichroic mirrors 121 a and 121 b and passesthrough an aperture 102G of the field stop 102. The apertures 102R, 102Gand 102B of the field stop 102 are formed like a belt (a rectangle), andthe light beams of red, green and blue are emitted adjacent to eachother from these apertures.

[0007] As shown in FIG. 8, the belt-like light beams of respectivecolors emitted from the field stop 102 pass through a scanning opticalsystem 105, then illuminate different regions of a singletransmission-type light valve (a display panel) 104 in a belt-likemanner. With an effect of a rotating prism 103 constituting the scanningoptical system 105, the belt-like light beams of red, green and bluescan the light valve 104 from the bottom to the top. When a belt-likeilluminated region of one of the light beams goes beyond the uppermostend of an effective region of the light valve 104, the belt-likeilluminated region of this light beam appears at the lowermost end ofthe effective region of the light valve 104 again. In this manner, thelight beams of red, green and blue can scan over the entire effectiveregion of the light valve 104 continuously. A light beam illuminatingeach row on the light valve 104 varies moment by moment, and a lightvalve driving device (not shown in this figure) drives each pixel by aninformation signal according to the color of the light beam that isilluminated. This means that each row of the light valve 104 is driventhree times for every field of a video signal to be displayed. A drivingsignal inputted to each row is a color signal corresponding to the lightbeam illuminating this row among signals of the image to be displayed.The light beams of these colors that have been modulated by the lightvalve 104 are magnified and projected onto a screen (not shown in thisfigure) by a projection lens 106.

[0008] With the above configuration, the light beam from the white lightsource is separated into light beams of three primary colors, so thatthe light from the light source can be used with substantially no lossand the efficiency of light utilization can be increased. Also, sinceeach of the pixels on the light valve displays red, green and bluesequentially, a convergence adjusting mechanism between the liquidcrystal panels as in the three-plate system is not necessary, andtherefore, it is possible to provide a high quality image.

[0009] However, in the above configuration, the light beams of thesecolors from the field stop 102 are not converged when transmitted by therotating prism 103. Since the size (the radius of gyration) of therotating prism 103 has to be in accordance with a region illuminated bythe light beam emitted from the field stop 102, the rotating prism 103becomes large and heavy. This has made it difficult to reduce the sizeand weight of the apparatus. Furthermore, a powerful motor for rotatingthe rotating prism 103 becomes necessary, causing an increase in thesize and cost of the apparatus.

[0010] Moreover, with the above-described configuration of the colorseparation optical system 101, the lengths of optical paths of the lightbeams of individual colors from the light source portion 100 to thelight valve 104 are not equal. Thus, it is impossible to focus all thelight beams at a pupil position of the projection lens 106. As a result,the light quantity of the light beam focused at the pupil position andthe light quantity of the light beam focused at a position shifted fromthe pupil position are different on the screen, resulting in poor coloruniformity in the displayed image.

DISCLOSURE OF INVENTION

[0011] It is an object of the present invention to solve theabove-described problems of the conventional image display apparatus andto provide a small projection-type image display apparatus that isprovided with a scanning optical system for scanning an illuminatedportion (a light valve) sequentially with light beams of individualcolors and has enhanced color uniformity in a displayed image.

[0012] In order to achieve the above-mentioned object, a projection-typeimage display apparatus of the present invention includes a light sourceportion for emitting a white light beam; a first optical system, whichincludes a white illumination optical system that the white light beamfrom the light source portion enters and that emits a uniform whiteillumination light beam having a rectangular cross-section, a colorseparation optical system for separating the white illumination lightbeam into respective light beams of red, green and blue, and a relaylens system that the respective light beams obtained by a colorseparation enter; a rotating polygon mirror that the respective lightbeams having left the relay lens system enter and that scans therespective light beams while reflecting the respective light beams; asecond optical system for leading the respective light beams reflectedby the rotating polygon mirror to an illumination position; an imagedisplay panel that is arranged at the illumination position and providedwith many pixels for modulating an incident light according to a colorsignal of red, green or blue; an image display panel driving circuit fordriving each of the pixels of the image display panel by a signalcorresponding to a color of light entering this pixel; and a projectionoptical system for magnifying and projecting an image of the imagedisplay panel. Here, the color separation optical system includes firstand second red-reflecting mirrors that reflect at least the red lightbeam, first and second green-reflecting mirrors that reflect at leastthe green light beam, and first and second blue-reflecting mirrors thatreflect at least the blue light beam. The mirrors are arranged so thatoptical paths of the respective light beams have equal lengths from thelight source portion to the rotating polygon mirror.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is a schematic view showing a configuration of opticalsystems of a projection-type image display apparatus according to afirst embodiment of the present invention.

[0014]FIG. 2 is a front view showing light source images formed on arotating polygon mirror of the projection-type image display apparatusshown in FIG. 1.

[0015]FIG. 3 is a schematic view showing a configuration of a colorseparation optical system of the projection-type image display apparatusaccording to the first embodiment of the present invention.

[0016]FIG. 4 is a schematic view showing a configuration of a colorseparation optical system of a projection-type image display apparatusaccording to a second embodiment of the present invention.

[0017]FIG. 5 is a schematic view showing a configuration of a colorseparation optical system of a projection-type image display apparatusaccording to a third embodiment of the present invention.

[0018]FIGS. 6A to 6F are drawings showing how light reflected by therotating polygon mirror changes and how light beams of individual colorsilluminating an image display panel are scanned in the projection-typeimage display apparatus shown in FIG. 1.

[0019]FIG. 7 is an exploded perspective view showing a configuration ofa transmission-type image display panel used in the projection-typeimage display apparatus shown in FIG. 1.

[0020]FIG. 8 is a schematic view showing a configuration of aconventional single-plate projection-type image display apparatus usinga scanning optical system.

[0021]FIG. 9 is a sectional view showing details of a color separationoptical system used in the projection-type image display apparatus shownin FIG. 8.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] A projection-type image display apparatus of the presentinvention displays a color image by using not a color filter but a lightvalve (an image display panel) having no pixel exclusively for a lightbeam of each color. This makes it possible to achieve a higherefficiency of light utilization and a higher resolution display.Furthermore, by constructing a scanning optical system with a rotatingpolygon mirror, a small image display apparatus can be provided.

[0023] Also, since optical paths of light beams of individual colorshave equal lengths from a light source portion to the rotating polygonmirror, it is possible to display an image with enhanced coloruniformity.

[0024] In the above-mentioned projection-type image display apparatus ofthe present invention, it is preferable that an effective portion ofeach of the respective light beams does not interfere with any of themirrors for reflecting the light beams of the other colors, and opticalaxes of the respective light beams do not intersect with each other onthe optical paths before the relay lens system.

[0025] Alternatively, it is preferable that an effective portion of atleast one light beam out of the light beams reflected respectively bythe first red-reflecting mirror, the first green-reflecting mirror andthe first blue-reflecting mirror interferes with the first reflectingmirror arranged in a foregoing stage of the first reflecting mirror thathas reflected the at least one light beam, an optical axis of each ofthe respective light beams intersects twice optical axes of the lightbeams of the other colors on the optical path before the relay lenssystem, and the first blue-reflecting mirror and the firstgreen-reflecting mirror respectively are a blue-reflectingred/green-transmitting dichroic mirror and a blue/green-reflectingred-transmitting dichroic mirror, and the light beam from the whiteillumination optical system enters the blue-reflectingred/green-transmitting dichroic mirror and the blue/green-reflectingred-transmitting dichroic mirror in this order.

[0026] Alternatively, it is preferable that an effective portion of atleast one light beam out of the light beams reflected respectively bythe first red-reflecting mirror, the first green-reflecting mirror andthe first blue-reflecting mirror interferes with the first reflectingmirror arranged in a foregoing stage of the first reflecting mirror thathas reflected the at least one light beam or interferes with the secondreflecting mirror for receiving the light beam reflected by the firstreflecting mirror arranged in a subsequent stage of the first reflectingmirror that has reflected the at least one light beam, an optical axisof each of the respective light beams intersects four times optical axesof the light beams of the other colors on the optical path before therelay lens system, and the first red-reflecting mirror and the firstgreen-reflecting mirror respectively are a red-reflectinggreen/blue-transmitting dichroic mirror and a red/green-reflectingblue-transmitting dichroic mirror, and the light beam from the whiteillumination optical system enters the red-reflectinggreen/blue-transmitting dichroic mirror and the red/green-reflectingblue-transmitting dichroic mirror in this order.

[0027] In the above-described projection-type image display apparatus ofthe present invention, it also is preferable that at least one dichroicfilter for enhancing color purity is provided between the colorseparation optical system and the rotating polygon mirror.

[0028] Further, it is preferable that the white illumination opticalsystem includes an integrator optical system for emitting a white lightbeam having a rectangular cross-section.

[0029] Moreover, it is preferable that the second optical systemincludes at least one fθ lens.

[0030] In addition, the image display panel may be a transmission-typelight valve. Alternatively, the image display panel may be areflection-type light valve.

[0031] The following is a specific description of the projection-typeimage display apparatus of the present invention, with reference topreferred embodiments.

[0032] (First Embodiment)

[0033]FIG. 1 is a schematic view showing a configuration of aprojection-type image display apparatus of a first embodiment of thepresent invention. The projection-type image display apparatus includesa light source portion 201, a white illumination optical system having arod integrator 202 and a first focusing lens 203, a color separationoptical system 204, a relay lens system having second focusing lenses205R, 205G and 205B provided for individual colors and a third focusinglens 206, a rotating polygon mirror 207, a second optical system 210having a fθ lens 211, an image display panel 212, an image display paneldriving circuit 217 and a projection optical system 216. The whiteillumination optical system, the color separation optical system 204 andthe relay lens system constitute a first optical system. Also, therotating polygon mirror 207 and the second optical system 210 constitutea scanning optical system.

[0034] A white light beam emitted from the light source portion 201formed of a concave mirror and a lamp bulb enters the rod integrator202, is reflected by its inner surface several times, becomes a whitelight beam with a substantially uniform intensity and a rectangularcross-section at a rectangular emitting-aperture portion of the rodintegrator 202, and then reaches the first focusing lens 203. The firstfocusing lens 203 is optically designed such that the emitting-apertureportion of the rod integrator 202 is an object point and an incidentsurface of each of the second focusing lenses 205R, 205G and 205B forrespective colors, which will be described later, is an image point. Thelight beam that has left the first focusing lens 203 is separated intored, green and blue light beams by the color separation optical system204 (described more specifically later), and focused onto the secondfocusing lenses 205R, 205G and 205B, respectively. The focused lightbeams respectively form light source images on a reflecting surface 208of the rotating polygon mirror 207 by the second focusing lenses 205R,205G and 205B for respective colors and the third focusing lens 206,which are optically designed such that a virtual image of theemitting-aperture portion of the rod integrator 202 is formed on thereflecting surface 208 of the rotating polygon mirror 207.

[0035] The rotating polygon mirror 207 is rotated continuously by amotor (not shown in this figure) about a rotation axis 209 in adirection indicated by an arrow 207 a. As in FIG. 2, which shows onemoment during the rotation of the rotating polygon mirror 207,rectangular groups (the above-mentioned light source images) 220 of red,blue and green lights are formed on one reflecting surface 208 so as tobe aligned along a moving direction of the reflecting surface 208 suchthat they are not overlapped.

[0036] The light beams of the respective colors reflected by thereflecting surface 208 of the rotating polygon mirror 207 travel via thesecond optical system 210, reach the image display panel 212 and thenare magnified and projected onto a screen (not shown in this figure) bythe projection optical system (only partially shown) 216.

[0037] The color separation optical system 204 of the present embodimentwill be described.

[0038] The light beam that has left the first focusing lens 203 isseparated into red, green and blue light beams by the color separationoptical system 204, and these light beams are focused such that opticalimages whose object points correspond to the emitting-aperture portionof the rod integrator 202 are formed on the respective surfaces of thesecond focusing lenses 205R, 205G and 205B. The angles of first dichroicmirrors and second dichroic mirrors constituting the color separationoptical system 204 and the spaces between them are adjusted so thatthese optical images are formed on the same plane.

[0039] In the case where the conventional color separation opticalsystem 101 as shown in FIG. 9 is provided in the subsequent stage of thefirst focusing lens 203, the optical images of the respective colorsfocused by the first focusing lens 203 and the color separation opticalsystem 101 cannot be positioned on the same plane. This is because thereis a difference between the optical path of the green light beam 134transmitted by the dichroic mirrors 121 a and 121 b and the opticalpaths of the blue light beam 132 reflected by the dichroic mirror 121 aand the total reflection mirror 121 d and the red light beam reflectedby the dichroic mirror 121 b and the total reflection mirror 121 c. Inother words, the positions on which the green light beam and the blueand red light beams are focused by the third focusing lens 206 do notmatch. Accordingly, in order for the virtual image of theemitting-aperture portion of the rod integrator 202 for each color to beformed on the reflecting surface 208 of the rotating polygon mirror 207,there is no alternative but to adopt the configuration of two opticalsystems having a relay lens system including a second focusing lens forgreen light and a third focusing lens for green light and a relay lenssystem including second focusing lenses for blue and red lights andthird focusing lenses for blue and red lights.

[0040] However, in the subsequent stage of the rotating polygon mirror207, since it is necessary to constitute the second optical system 210formed of the fθ lens 211 by one optical system so that a scanning angleof each light beam scanned by the rotating polygon mirror 207 and aheight of an image formed on the image display panel 212 areproportional, the above-mentioned configuration of the two opticalsystems for the green light and the blue and red lights cannot beachieved. Thus, it is impossible to achieve a series of optical systemsfrom the light source portion 201 to the image display panel 212 byusing the conventional color separation optical system 101 as shown inFIG. 9.

[0041] For the above reason, in the color separation optical system 204in the first embodiment, as shown in FIG. 3, the angles of the firstdichroic mirrors 301R, 301B and 301G and the second dichroic mirrors302R, 302G and 302B constituting the color separation optical system 204and the spaces between them are adjusted so that the optical paths ofthe respective colors have equal lengths from the light source portion201 to the rotating polygon mirror 207, i.e., so that the optical imagesfocused onto the surfaces of the second focusing lenses 205R, 205G and205B are on the same plane. However, although the color separationoptical system 204 is constituted so that the incident surfaces of thesecond focusing lenses 205R, 205G and 205B for individual colors are onthe same plane in the present embodiment, the color separation opticalsystem 204 also may be constituted so that emitting surfaces of thesecond focusing lenses 205R, 205G and 205B are on the same plane.

[0042] The following is a description of a specific arrangement andoptical characteristics of the first dichroic mirrors 301R, 301B and301G and the second dichroic mirrors 302R, 302G and 302B, with referenceto FIG. 3. In FIG. 3, W, R, G and B indicate optical axes of a whitelight beam, a red light beam, a green light beam and a blue light beam,respectively.

[0043] The first dichroic mirror 301R, the first dichroic mirror 301Gand the first dichroic mirror 301B are arranged in this order from theincident side of the white light beam that has left the first focusinglens 203.

[0044] The first dichroic mirror 301R is inclined by about 550 withrespect to a plane perpendicular to the optical axis and has a functionof reflecting red light and transmitting blue and green lights in thevisible spectrum. The second dichroic mirror 302R that the lightreflected by the first dichroic mirror 301R enters also has opticalcharacteristics similar to the first dichroic mirror 301R and isarranged in parallel with the first dichroic mirror 301R.

[0045] Also, the first dichroic mirror 301G is inclined by about 300with respect to a plane perpendicular to the optical axis and has afunction of reflecting green light and transmitting blue light in thevisible spectrum. The second dichroic mirror 302G that the lightreflected by the first dichroic mirror 301G enters also has opticalcharacteristics similar to the first dichroic mirror 301G and isarranged in parallel with the first dichroic mirror 301G.

[0046] Further, the first dichroic mirror 301B is inclined by about 45°with respect to a plane perpendicular to the optical axis and has afunction of reflecting blue light in the visible spectrum. The seconddichroic mirror 302B that the light reflected by the first dichroicmirror 301B enters also has optical characteristics similar to the firstdichroic mirror 301B and is arranged in parallel with the first dichroicmirror 301B.

[0047] In addition, an effective portion of each of the light beams ofthree colors obtained by the color separation does not interfere withthe first or second dichroic mirror for reflecting the light beams ofthe other colors. Here, the “effective portion” of the light beam refersto a portion in a light beam of each color that reaches an effectivepixel region of the image display panel 212 and contributes to a colorimage formation. For example, in the case of a red light beam reflectedsequentially by the first dichroic mirror 301R and the second dichroicmirror 302R, the effective portion of this red light beam does notinterfere with any of the first dichroic mirror 301G and the seconddichroic mirror 302G that reflect the green light beam and the firstdichroic mirror 301B and the second dichroic mirror 302B that reflectthe blue light beam. Similarly, the effective portion of the green lightbeam does not interfere with any of the first dichroic mirror 301R andthe second dichroic mirror 302R that reflect the red light beam and thefirst dichroic mirror 301B and the second dichroic mirror 302B thatreflect the blue light beam. Also, the effective portion of the bluelight beam does not interfere with any of the first dichroic mirror 301Rand the second dichroic mirror 302R that reflect the red light beam andthe first dichroic mirror 301G and the second dichroic mirror 302G thatreflect the green light beam.

[0048] Moreover, the optical axes of these light beams do not intersectwith each other on the optical paths before reaching the second focusinglenses 205R, 205G and 205B for the individual colors. In other words, asshown in FIG. 3 seen in a direction normal to a plane including theoptical axes of these light beams, the optical axis R of the red light,the optical axis G of the green light and the optical axis B of the bluelight do not intersect with each other.

[0049] As long as the effective portion of a light beam of each colordoes not interfere with any of the first and second dichroic mirrors forreflecting the light beams of the other colors and the optical axes ofthese light beams do not intersect with each other, the angles of thefirst and second dichroic mirrors and the spaces between them are notlimited to the above example.

[0050] Also, the optical characteristics regardingreflection/transmission of the first dichroic mirrors and the seconddichroic mirrors are not limited to the above example, and several kindsof combinations are possible. In order to reduce costs, a configurationin which no problem arises in the optical characteristics of the emittedlight beams of individual colors may be adopted; for example, the firstdichroic mirror 301B and the second dichroic mirrors 302R, 302G and 302Bmay be replaced with total reflection mirrors.

[0051] Furthermore, for the purpose of achieving an excellent colorpurity of each light beam, a dichroic filter may be inserted on theoptical path between the color separation optical system 204 and therotating polygon mirror 207. Such a dichroic filter may be provided asan independent member or by applying a coating having a dichroic filterfunction to the surface of the second focusing lens for each light beam.

[0052] Next, when the rotating polygon mirror 207 is rotated, how areflected light changes in the reflecting surface 208 and how the lightbeams of individual colors entering the image display panel 212 arescanned will be described by way of FIGS. 6A to 6F.

[0053]FIGS. 6A to 6F show the rotation of the rotating polygon mirror207 and an accompanying change in the state of the image display panel212 illuminated by the light beams of individual colors at a fixed timeinterval. In the figures showing the illumination states of the imagedisplay panel 212 located above, R, G and B represent regionsilluminated by the red light, the green light and the blue light,respectively. In the figures showing the rotation of the rotatingpolygon mirror 207 and reflection states of the light beams ofindividual colors located below, R, G and B indicate chief rays of redlight, green light and blue light respectively, and arrows indicate thetraveling directions of these rays.

[0054] At time T=μl (see FIG. 6A), the light beams of red, green andblue enter the same reflecting surface 208 a of the rotating polygonmirror 207. At this time, the incident angles of the blue, green and redlight beams to the reflecting surface 208 a (the angles that the chiefrays of the incident light beams form with the normal line of thereflecting surface 208 a) decrease in this order. Thus, the blue lightbeam is reflected at the largest angle toward the top of the drawing,the green light beam is reflected at a slightly smaller angle than theblue light beam, and the red light beam is reflected at a still smallerangle than the green light beam. Accordingly, the light beams of thesecolors enter the fθ lens 211 of the second optical system 210 atdifferent angles from each other. In the second optical system 210, aheight of a light beam at an illumination position (the image displaypanel 212) is determined depending on the incident angle of the lightbeam. Therefore, the light beams of the respective colors form images ofthe second focusing lenses 205R, 205G and 205B at different positions onthe image display panel 212 as indicated by the figure. In other words,the region illuminated by the blue light, the region illuminated by thegreen light and the region illuminated by the red light are formed onthe image display panel 212 in this order from the top.

[0055] At time T=t2 (see FIG. 6B), which is the time the rotatingpolygon mirror 207 has been rotated by a predetermined angle from theposition at time T=t1, the red light beam and the green light beam enterthe same reflecting surface 208 a of the rotating polygon mirror 207,while the blue light beam enters a reflecting surface 208 b that hasjust arrived at this entering position. At this time, with respect tothe blue light beam in particular, since the incident angle of thislight beam into the reflecting surface changes considerably from thestate at time T=t1, its reflection direction also changes considerably.Accordingly, the green light beam is reflected at the largest angletoward the top of the drawing, the red light beam is reflected at aslightly smaller angle than the green light beam, and the blue lightbeam is reflected at a still smaller angle than the red light beam.Therefore, the light beams of the respective colors form images of thesecond focusing lenses 205R, 205G and 205B at different positions on theimage display panel 212 as indicated by the figure. In other words, theregion illuminated by the green light, the region illuminated by the redlight and the region illuminated by the blue light are formed on theimage display panel 212 in this order from the top.

[0056] At time T=t3 (see FIG. 6C), which is the time the rotatingpolygon mirror 207 has been further rotated by a predetermined anglefrom the position at time T=t2, only the red light beam enters thereflecting surface 208 a, while the green light beam and the blue lightbeam enter the same reflecting surface 208 b. At this time, with respectto the green light beam in particular, since the incident angle of thislight beam into the reflecting surface changes considerably from thestate at time T=t2, its reflection direction also changes considerably.Accordingly, the red light beam is reflected at the largest angle towardthe top of the drawing, the blue light beam is reflected at a slightlysmaller angle than the red light beam, and the green light beam isreflected at a still smaller angle than the blue light beam. Therefore,the light beams of the respective colors form images of the secondfocusing lenses 205R, 205G and 205B at different positions on the imagedisplay panel 212 as indicated by the figure. In other words, the regionilluminated by the red light, the region illuminated by the blue lightand the region illuminated by the green light are formed on the imagedisplay panel 212 in this order from the top.

[0057] At time T=t4 (see FIG. 6D), which is the time the rotatingpolygon mirror 207 has been further rotated by a predetermined anglefrom the position at time T=t3, the light beams of red, green and blueenter the same reflecting surface 208 b. At this time, the positionalrelationship is the same as that at time T=t1 (see FIG. 6A), and thestate of the image display panel 212 illuminated by the light beams ofthese colors also is the same.

[0058] At time T=t5 (see FIG. 6E), which is the time the rotatingpolygon mirror 207 has been further rotated by a predetermined angle,the red light beam and the green light beam enter the same reflectingsurface 208 b, while the blue light beam enters a reflecting surface 208c that has just arrived at this entering position. At this time, thepositional relationship is the same as that at time T=t2 (see FIG. 6B),and the state of the image display panel 212 illuminated by the lightbeams of these colors also is the same.

[0059] At time T=t6 (see FIG. 6F), which is the time the rotatingpolygon mirror 207 has been further rotated by a predetermined angle,the red light beam enters the reflecting surface 208 b, while the greenlight beam and the blue light beam enter the same reflecting surface 208c. At this time, the positional relationship is the same as that at timeT=t3 (see FIG. 6C), and the state of the image display panel 212illuminated by the light beams of these colors also is the same.

[0060] As described above, the belt-like regions illuminated by thelight beams of red, green and blue that are formed on the image displaypanel 212 move sequentially in a scanning direction 212 a. AlthoughFIGS. 6A to 6F showed only the specific period (time T=t1 to t6) in theabove description, because of a continuous rotation of the rotatingpolygon mirror 207, each of the regions illuminated by the light beamsof the individual colors moves (is scanned) on the image display panel212 continuously upward (in the scanning direction 212 a). When theregion illuminated by the light beam reaches the upper end, it returnsto the lower end and moves upward again. A continuous switching of thetimes t1 to t6 described above at an even time interval allows anillumination with enhanced color uniformity and brightness uniformityand reduced flicker.

[0061] The second optical system 210 is formed of an optical systemhaving a function of the fθ lens and that of changing the magnificationfor forming an appropriate illuminated region on the image display panel212.

[0062] As shown in FIG. 7, the image display panel 212 includes atransmission-type liquid crystal panel 213, an entrance-side polarizingplate 214 as a polarizer provided on the entrance-side and an exit-sidepolarizing plate 215 as an analyzer provided on the exit side. Theentrance-side polarizing plate 214 is designed, for example, to transmitlight polarized in a shorter side direction 214 a of its rectangularoutline and to absorb light polarized in a direction orthogonal thereto.The light transmitted by the entrance-side polarizing plate 214 entersthe liquid crystal panel 213. The liquid crystal panel 213 has manypixels formed and arranged therein and is capable of changing thepolarization direction of the transmitted light at every pixel apertureby an external signal. In this configuration, the liquid crystal panel213 transmits the incident light while rotating its polarizationdirection by 90° when the pixels are not driven, whereas it transmitsthe incident light without changing the polarization direction when thepixels are driven. The exit-side polarizing plate 215 has polarizationcharacteristics in a direction orthogonal to the entrance-sidepolarizing plate 214. In other words, the exit-side polarizing plate 215has a transmission axis in a longer side direction 215 a of itsrectangular outline and transmits light polarized in this direction.Thus, the light that has entered an undriven pixel of the liquid crystalpanel 213 and been transmitted with its polarization direction rotatedby 90° can pass through this exit-side polarizing plate 215 because itis polarized in a direction parallel to the transmission axis of theexit-side polarizing plate 215. On the other hand, the light that hasentered a driven pixel of the liquid crystal panel 213 and beentransmitted without being subjected to the change in its polarizationdirection is absorbed by this exit-side polarizing plate 215 because itis polarized in a direction orthogonal to the transmission axis of theexit-side polarizing plate 215.

[0063] The image display panel driving circuit 217 drives each pixel ofthe liquid crystal panel 213 of the image display panel 212 by a signalcorresponding to the color of light illuminating this pixel. In thismanner, an image is formed by modulating the light at every pixel. Thelight transmitted by the image display panel 212 is projected onto ascreen (not shown in this figure) via a projection optical member 216.Since the scannings of the light beams of the individual colors shown inFIGS. 6A to 6F are carried out at a high speed (it is preferable thatone unit consisting of FIGS. 6A to 6F is carried out at least oncewithin one field period), images of individual colors are synthesized soas to be perceived by a retina of an observer as a color image that doesnot look separate.

[0064] As described above, the light beams of individual colors are madeto enter the rotating polygon mirror 207 at different incident anglesand different incident positions, and the reflected light beams are ledto the image display panel 204 via the second optical system having thefθ lens function, making it possible to display a color image even whenusing one image display panel 212 that has no color selection membersuch as a color filter and no pixel provided exclusively for a lightbeam of each color. In addition, since each pixel of the image displaypanel 212 displays the image according to the color of lightilluminating this pixel, a high resolution display can be achieved.Furthermore, since the light from the light source portion 201 always isled to the image display panel 204 effectively, it is possible toachieve a highly efficient light utilization.

[0065] Moreover, by constituting the optical system so as to obtainsmaller light source images on the reflecting surface 208 of therotating polygon mirror, the area of the reflecting surface 208 can bemade smaller. Accordingly, it becomes possible to reduce the size of therotating polygon mirror 207, allowing a smaller motor for rotating thisrotating polygon mirror. As a result, it becomes possible to reduce thesize, weight and cost of the entire apparatus.

[0066] In addition, since the color separation optical system 204 isconstituted such that the optical paths of the light beams of individualcolors have equal lengths from the light source portion 201 to therotating polygon mirror 207, a color image with enhanced coloruniformity can be displayed.

[0067] (Second Embodiment)

[0068]FIG. 4 shows a schematic configuration of the color separationoptical system 204 according to the present embodiment. In FIG. 4, W, R,G and B indicate optical axes of a white light beam, a red light beam, agreen light beam and a blue light beam, respectively. The presentembodiment is different from the first embodiment in the following twopoints.

[0069] First, a part of the effective portion of a light beam reflectedby a first dichroic mirror 401G interferes with a first dichroic mirror401B arranged in the foregoing stage (on the incident side of the whitelight beam) of the first dichroic mirror 401G. Also, a part of theeffective portion of a light beam reflected by a first dichroic mirror401R interferes with the first dichroic mirror 401G arranged in theforegoing stage of the first dichroic mirror 401R.

[0070] Second, the optical axis of a light beam of each color intersectstwice the optical axes of light beams of the other colors on the opticalpath before the second focusing lens 205R, 205G or 205B.

[0071] In the present embodiment, the above-described configurationespecially makes it possible to reduce the area in which the three firstdichroic mirrors are arranged. As a result, the area that theconfiguration of the color separation optical system 204 occupies can bemade compact, down to about two-thirds of that in the first embodiment.However, the optical characteristics thereof are limited. The followingis a description of the present embodiment, in particular, the colorseparation optical system 204.

[0072] The first dichroic mirror 401B, the first dichroic mirror 401Gand the first dichroic mirror 401R are arranged in this order from theincident side of the white light beam that has left the first focusinglens 203.

[0073] The first dichroic mirror 401B is inclined by about 20° withrespect to a plane perpendicular to the optical axis and has a functionof reflecting blue light and transmitting green and red lights in thevisible spectrum. A second dichroic mirror 402B that the light reflectedby the first dichroic mirror 401B enters also has opticalcharacteristics similar to the first dichroic mirror 401B and isarranged in parallel with the first dichroic mirror 401B.

[0074] Also, the first dichroic mirror 401G is inclined by about 40°with respect to a plane perpendicular to the optical axis and has afunction of reflecting green light and transmitting red light in thevisible spectrum. A second dichroic mirror 402G that the light reflectedby the first dichroic mirror 401G enters also has opticalcharacteristics similar to the first dichroic mirror 401G and isarranged in parallel with the first dichroic mirror 401G.

[0075] Further, the first dichroic mirror 401R is inclined by about 35°with respect to a plane perpendicular to the optical axis and has afunction of reflecting red light in the visible spectrum. A seconddichroic mirror 402R that the light reflected by the first dichroicmirror 401R enters also has optical characteristics similar to the firstdichroic mirror 401R and is arranged in parallel with the first dichroicmirror 401R.

[0076] Here, the blue light beam reflected by the first dichroic mirror401B is reflected by the second dichroic mirror 402B in a similarmanner, and then directed toward the second focusing lens 205B. Amongthe light beams transmitted by the first dichroic mirror 401B, the greenlight beam is reflected by the first dichroic mirror 401G and directedtoward the second dichroic mirror 402G. On the way, a part of theeffective portion of this green light beam directed toward the seconddichroic mirror 402G interferes with the first dichroic mirror 401B.However, since the first dichroic mirror 401B has opticalcharacteristics of shifting its spectral characteristics indicatingreflection or transmission on a shorter wavelength side when an incidentangle of a light beam (here, the incident angle refers to an angle thatan incident light beam forms with a plane perpendicular to the dichroicmirror) increases, the green light beam entering the first dichroicmirror 401B from its back surface is not completely blocked although theinterfering portion of this light beam decreases by less than about 10%corresponding to transmittance of the first dichroic mirror 401B.

[0077] Similarly, the red light beam transmitted by the first dichroicmirror 401G is reflected by the first dichroic mirror 401R and directedtoward the second dichroic mirror 402R. On the way, a part of theeffective portion of this red light beam directed toward the seconddichroic mirror 402R interferes with the first dichroic mirror 401G.However, since the first dichroic mirror 401G has opticalcharacteristics of shifting its spectral characteristics indicatingreflection or transmission on a shorter wavelength side when an incidentangle of a light beam (here, the incident angle refers to an angle thatan incident light beam forms with a plane perpendicular to the dichroicmirror) increases, the red light beam entering the first dichroic mirror401G from its back surface is not completely blocked although theinterfering portion of this light beam decreases by less than about 10%corresponding to transmittance of the first dichroic mirror 401G.

[0078] Furthermore, in the present embodiment, the optical axis of alight beam of each color intersects twice the optical axes of lightbeams of the other colors on the optical path before reaching the secondfocusing lens 205R, 205G or 205B for each color. In other words, asshown in FIG. 4 seen in a direction normal to a plane including theoptical axes of these light beams, the optical axis R of the red light,the optical axis G of the green light and the optical axis B of the bluelight each intersects once the optical axis of each of the light beamsof the other colors (twice in total).

[0079] Moreover, as in the first embodiment, the angles of the dichroicmirrors and the spaces between them are adjusted such that the opticalpaths of the light beams of individual colors have equal lengths fromthe light source portion 201 to the rotating polygon mirror 207.

[0080] In the present embodiment, the effective portion of a light beamof one color reflected by the first dichroic mirror interferes with thefirst dichroic mirror for reflecting the light beam of the other colorarranged in the foregoing stage (on the incident side of the white lightbeam W) of the first dichroic mirror that has reflected the light beamof that color. Furthermore, the optical axis of a light beam of eachcolor intersects twice the optical axes of light beams of the othercolors on the optical path before reaching the second focusing lens205R, 205G or 205B. Although it is necessary to adjust the angles of thefirst and second dichroic mirrors and the spaces between them forachieving the above configuration, the angles of the first and seconddichroic mirrors and the spaces between them are not limited to theabove example.

[0081] Also, the optical characteristics regardingreflection/transmission of the first dichroic mirrors and the seconddichroic mirrors are not limited to the above example, and several kindsof combinations are possible. In order to reduce costs, a configurationin which no problem arises in the optical characteristics of the emittedlight beams of individual colors may be adopted; for example, the firstdichroic mirror 401R and the second dichroic mirrors 402B, 402G and 402Rmay be replaced with total reflection mirrors.

[0082] Furthermore, for the purpose of achieving an excellent colorpurity of each light beam, a dichroic filter may be inserted on theoptical path between the color separation optical system 204 and therotating polygon mirror 207. Such a dichroic filter may be provided asan independent member or by applying a coating having a dichroic filterfunction to the surface of the second focusing lens for each light beam.

[0083] Except for the configuration of the color separation opticalsystem 204 being different as described above, a projection-type imagedisplay apparatus of the present embodiment can be constituted in asimilar manner as in the first embodiment.

[0084] According to the present embodiment, it is possible to provide aprojection-type image display apparatus having characteristics similarto those of the first embodiment. Moreover, the present embodiment canprovide a smaller projection-type image display apparatus than the firstembodiment.

[0085] (Third Embodiment)

[0086]FIG. 5 shows a schematic configuration of the color separationoptical system 204 according to the present embodiment. In FIG. 5, W, R,G and B indicate optical axes of a white light beam, a red light beam, agreen light beam and a blue light beam, respectively. The presentembodiment is different from the first embodiment in the following twopoints.

[0087] First, a part of the effective portion of a light beam reflectedby a first dichroic mirror 501R interferes with a second dichroic mirror502G. Also, a part of the effective portion of a light beam reflected bya first dichroic mirror 501G interferes with the first dichroic mirror501R arranged in the foregoing stage (on the incident side of the whitelight beam) of the first dichroic mirror 501G and interferes with thesecond dichroic mirror 502B. Further, a part of the effective portion ofa light beam reflected by a first dichroic mirror 501B interferes withthe first dichroic mirrors 501R and 501G arranged in the foregoing stageof the first dichroic mirror 501B.

[0088] Second, the optical axis of a light beam of each color intersectsfour times the optical axes of light beams of the other colors on theoptical path before the second focusing lens 205R, 205G or 205B.

[0089] In the present embodiment, the above-described configurationmakes it possible to reduce both the area in which the three firstdichroic mirrors are arranged and the area in which the three seconddichroic mirrors are arranged. As a result, the area that theconfiguration of the color separation optical system 204 occupies can bemade compact, down to about half of that in the first embodiment.However, the optical characteristics thereof are limited. The followingis a description of the present embodiment, in particular, the colorseparation optical system 204.

[0090] The first dichroic mirror 501R, the first dichroic mirror 501Gand the first dichroic mirror 501B are arranged in this order from theincident side of the white light beam that has left the first focusinglens 203.

[0091] The first dichroic mirror 501R is inclined by about 55° withrespect to a plane perpendicular to the optical axis and has a functionof reflecting red light and transmitting green and blue lights in thevisible spectrum. A second dichroic mirror 502R that the light reflectedby the first dichroic mirror 501R enters also has opticalcharacteristics similar to the first dichroic mirror 501R and isarranged in parallel with the first dichroic mirror 501R.

[0092] Also, the first dichroic mirror 501G is inclined by about 35°with respect to a plane perpendicular to the optical axis and has afunction of reflecting green light and transmitting blue light in thevisible spectrum. A second dichroic mirror 502G that the light reflectedby the first dichroic mirror 501G enters also has opticalcharacteristics similar to the first dichroic mirror 501G and isarranged in parallel with the first dichroic mirror 501G.

[0093] Further, the first dichroic mirror 501B is inclined by about 200with respect to a plane perpendicular to the optical axis and has afunction of reflecting blue light in the visible spectrum. A seconddichroic mirror 502B that the light reflected by the first dichroicmirror 501B enters also has optical characteristics similar to the firstdichroic mirror 501B and is arranged in parallel with the first dichroicmirror 501B.

[0094] Here, the red light beam reflected by the first dichroic mirror501R is reflected by the second dichroic mirror 502R in a similarmanner, and then directed toward the second focusing lens 205R. On theway, a part of the effective portion of the red light beam directedtoward the second dichroic mirror 502R interferes with the seconddichroic mirror 502G. However, since the second dichroic mirror 502G hasoptical characteristics of shifting its spectral characteristicsindicating reflection or transmission on a shorter wavelength side whenan incident angle of a light beam (here, the incident angle refers to anangle that an incident light beam forms with a plane perpendicular tothe dichroic mirror) increases, the red light beam entering the seconddichroic mirror 502G is not completely blocked although the interferingportion of this light beam decreases by less than about 10%corresponding to transmittance of the second dichroic mirror 502G.

[0095] Among the light beams transmitted by the first dichroic mirror501R, the green light beam is reflected by the first dichroic mirror501G and directed toward the second dichroic mirror 502G. On the way, apart of the effective portion of this green light beam directed towardthe second dichroic mirror 502G interferes with the first dichroicmirror 501R and the second dichroic mirror 502B. However, since thefirst dichroic mirror 501R has optical characteristics of shifting itsspectral characteristics indicating reflection or transmission on alonger wavelength side when an incident angle of a light beam (here, theincident angle refers to an angle that an incident light beam forms witha plane perpendicular to the dichroic mirror) decreases, the green lightbeam entering the first dichroic mirror 501R from its back surface isnot completely blocked although the interfering portion of this lightbeam decreases by less than about 10% corresponding to transmittance ofthe first dichroic mirror 501R. Also, since the second dichroic mirror502B has optical characteristics of shifting its spectralcharacteristics indicating reflection or transmission on a shorterwavelength side when an incident angle of a light beam (here, theincident angle refers to an angle that an incident light beam forms witha plane perpendicular to the dichroic mirror) increases, the green lightbeam entering the second dichroic mirror 502B is not completely blockedalthough the interfering portion of this light beam decreases by lessthan about 10% corresponding to transmittance of the second dichroicmirror 502B.

[0096] Moreover, the blue light beam transmitted by the first dichroicmirror 501G is reflected by the first dichroic mirror 501B and directedtoward the second dichroic mirror 502B. On the way, a part of theeffective portion of this blue light beam directed toward the seconddichroic mirror 502B interferes with the first dichroic mirrors 501G and501R. However, since the first dichroic mirrors 501G and 501R haveoptical characteristics of shifting their spectral characteristicsindicating reflection or transmission on a longer wavelength side whenan incident angle of a light beam (here, the incident angle refers to anangle that an incident light beam forms with a plane perpendicular tothe dichroic mirror) decreases, the blue light beam entering the firstdichroic mirrors 501G and 501R from their back surfaces is notcompletely blocked although the interfering portion of this light beamdecreases by less than about 10% corresponding to transmittances of thefirst dichroic mirrors 501G and 501R.

[0097] Furthermore, in the present embodiment, the optical axis of alight beam of each color intersects four times the optical axes of lightbeams of the other colors on the optical path before the second focusinglens 205R, 205G or 205B for each color. In other words, as shown in FIG.5 seen in a direction normal to a plane including the optical axes ofthese light beams, the optical axis R of the red light, the optical axisG of the green light and the optical axis B of the blue light eachintersects twice the optical axis of each of the light beams of theother colors (four times in total).

[0098] Moreover, as in the first embodiment, the angles of the dichroicmirrors and the spaces between them are adjusted such that the opticalpaths of the light beams of individual colors have equal lengths fromthe light source portion 201 to the rotating polygon mirror 207.

[0099] In the present embodiment, the effective portion of a light beamof one color reflected by the first dichroic mirror interferes with thefirst dichroic mirrors for reflecting the light beam of the other colorsarranged in the foregoing stage (on the incident side of the white lightbeam W) of the first dichroic mirror that has reflected the light beamof that color. Alternatively, the effective portion of a light beam ofone color reflected by the first dichroic mirror interferes with thesecond dichroic mirror for receiving the light beam of the other colorreflected by the first dichroic mirror arranged in the subsequent stage(on the side opposite to the incident side of the white light beam W) ofthe first dichroic mirror that has reflected the light beam of thatcolor. Furthermore, the optical axis of a light beam of each colorintersects four times the optical axes of light beams of the othercolors on the optical path before the second focusing lens 205R, 205G or205B. Although it is necessary to adjust the angles of the first andsecond dichroic mirrors and the spaces between them for achieving theabove configuration, the angles of the first and second dichroic mirrorsand the spaces between them are not limited to the above example.

[0100] Also, the optical characteristics regardingreflection/transmission of the first dichroic mirrors and the seconddichroic mirrors are not limited to the above example, and several kindsof combinations are possible. In order to reduce costs, a configurationin which no problem arises in the optical characteristics of the emittedlight beams of individual colors may be adopted; for example, the firstdichroic mirror 501B and the second dichroic mirror 502R may be replacedwith total reflection mirrors.

[0101] Furthermore, for the purpose of achieving an excellent colorpurity of each light beam, a dichroic filter may be inserted on theoptical path between the color separation optical system 204 and therotating polygon mirror 207. Such a dichroic filter may be provided asan independent member or by applying a coating having a dichroic filterfunction to the surface of the second focusing lens for each light beam.

[0102] Except for the configuration of the color separation opticalsystem 204 being different as described above, a projection-type imagedisplay apparatus of the present embodiment can be constituted in asimilar manner as in the first embodiment.

[0103] According to the present embodiment, it is possible to provide aprojection-type image display apparatus having characteristics similarto those of the first embodiment. Moreover, the present embodiment canprovide a smaller projection-type image display apparatus than not onlythe first embodiment but also the second embodiment.

[0104] Although a transmission-type liquid crystal system display devicewas used as the image display panel 212 in the above embodiments, anydevice is appropriate as long as it is a display device that displays animage by modulating an incident light. Thus, it also is possible to usea reflection-type liquid crystal system, a reflection-type mirror deviceor the like. Needless to say, it has to be a display device capable offast response.

[0105] In addition, although the above embodiments were directed to anexample of using the rod integrator 202 having a rectangular emittingaperture as the integrator optical system, the present invention is notlimited to this as long as a uniform white illumination light beamhaving a rectangular cross-section can be emitted. For example, it maybe possible to use an integrator optical system having a first microlensarray, which is a group of microlenses having identically-shapedrectangular apertures, and a second lens array, which is a group ofmicrolenses in a one-to-one correspondence with the microlenses of thefirst lens array.

[0106] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Theembodiments disclosed in this application are to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims rather than by the foregoingdescription, all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

1. A projection-type image display apparatus, comprising: a light sourceportion for emitting a white light beam; a first optical systemcomprising a white illumination optical system that the white light beamfrom the light source portion enters and that emits a uniform whiteillumination light beam having a rectangular cross-section, a colorseparation optical system for separating the white illumination lightbeam into respective light beams of red, green and blue, and a relaylens system that the respective light beams obtained by a colorseparation enter; a rotating polygon mirror that the respective lightbeams having left the relay lens system enter and that scans therespective light beams while reflecting the respective light beams; asecond optical system for leading the respective light beams reflectedby the rotating polygon mirror to an illumination position; an imagedisplay panel that is arranged at the illumination position and providedwith many pixels for modulating an incident light according to a colorsignal of red, green or blue; an image display panel driving circuit fordriving each of the pixels of the image display panel by a signalcorresponding to a color of light entering this pixel; and a projectionoptical system for magnifying and projecting an image of the imagedisplay panel; wherein the color separation optical system comprisesfirst and second red-reflecting mirrors that reflect at least the redlight beam, first and second green-reflecting mirrors that reflect atleast the green light beam, and first and second blue-reflecting mirrorsthat reflect at least the blue light beam, and the mirrors are arrangedso that optical paths of the respective light beams have equal lengthsfrom the light source portion to the rotating polygon mirror.
 2. Theprojection-type image display apparatus according to claim 1, wherein aneffective portion of each of the respective light beams does notinterfere with any of the mirrors for reflecting the light beams of theother colors, and optical axes of the respective light beams do notintersect with each other on the optical paths before reaching the relaylens system.
 3. The projection-type image display apparatus according toclaim 1, wherein an effective portion of at least one light beam out ofthe light beams reflected respectively by the first red-reflectingmirror, the first green-reflecting mirror and the first blue-reflectingmirror interferes with the first reflecting mirror arranged in aforegoing stage of the first reflecting mirror that has reflected the atleast one light beam, an optical axis of each of the respective lightbeams intersects twice optical axes of the light beams of the othercolors on the optical path before the relay lens system, and the firstblue-reflecting mirror and the first green-reflecting mirrorrespectively are a blue-reflecting red/green-transmitting dichroicmirror and a blue/green-reflecting red-transmitting dichroic mirror, andthe light beam from the white illumination optical system enters theblue-reflecting red/green-transmitting dichroic mirror and theblue/green-reflecting red-transmitting dichroic mirror in this order. 4.The projection-type image display apparatus according to claim 1,wherein an effective portion of at least one light beam out of the lightbeams reflected respectively by the first red-reflecting mirror, thefirst green-reflecting mirror and the first blue-reflecting mirrorinterferes with the first reflecting mirror arranged in a foregoingstage of the first reflecting mirror that has reflected the at least onelight beam or interferes with the second reflecting mirror for receivingthe light beam reflected by the first reflecting mirror arranged in asubsequent stage of the first reflecting mirror that has reflected theat least one light beam, an optical axis of each of the respective lightbeams intersects four times optical axes of the light beams of the othercolors on the optical path before the relay lens system, and the firstred-reflecting mirror and the first green-reflecting mirror respectivelyare a red-reflecting green/blue-transmitting dichroic mirror and ared/green-reflecting blue-transmitting dichroic mirror, and the lightbeam from the white illumination optical system enters thered-reflecting green/blue-transmitting dichroic mirror and thered/green-reflecting blue-transmitting dichroic mirror in this order. 5.The projection-type image display apparatus according to claim 1,wherein at least one dichroic filter for enhancing color purity isprovided between the color separation optical system and the rotatingpolygon mirror.
 6. The projection-type image display apparatus accordingto claim 1, wherein the white illumination optical system comprises anintegrator optical system for emitting a white light beam having arectangular cross-section.
 7. The projection-type image displayapparatus according to claim 1, wherein the second optical systemcomprises at least one fθ lens.
 8. The projection-type image displayapparatus according to claim 1, wherein the image display panel is atransmission-type light valve.
 9. The projection-type image displayapparatus according to claim 1, wherein the image display panel is areflection-type light valve.